You were the daughter of Muzan, a mix between to species and while you could survive under the sun because of that it did burn your skin

You loathed your Father greatly, having killed your Mother and tried to pressure his ideals on you, that's why you were now here, with Shinobou in her estate

Of course you never revealed who or what you were, you enjoyed being with her as her all

"I would recommend some sunscreen if you're so sensitive to the sun"